Execute "conan install" also when running from "conan build"

[petermbauer]

Hi,

according to https://github.com/conan-io/cmake-conan/blob/develop/conan.cmake#L486 nothing happens if CMake is called by the CMake helper during a "conan build" command assuming that the user must have already run "conan install" before. The problem with this is that if the conanfile.py has changed and the user runs another "conan build", conan.cmake also does not do a "conan install" though it would be needed. Would it be possible to check for CONAN_IN_LOCAL_CACHE instead of CONAN_EXPORTED so it also works when using conan build only?

br, Peter